Thermal inkjet print cartridges operate by rapidly heating a small volume of ink to cause the ink to vaporize and be ejected through one of a plurality of orifices so as to print a dot of ink on a recording medium, such as a sheet of paper. The properly sequenced ejection of ink from each orifice causes characters or other images to be printed upon the paper as the printhead is moved relative to the paper.
A conventional inkjet printhead generally includes: (1) ink channels to supply ink from an ink reservoir to each vaporization chamber proximate to an orifice; (2) a metal orifice plate or nozzle member in which the orifices are formed in the required pattern; and (3) a silicon substrate containing a series of thin film resistors, one resistor per vaporization chamber.
To print a single dot of ink, an electrical current from an external power supply is passed through a selected thin film resistor. The resistor is thereby heated, in turn superheating a thin layer of the adjacent ink within a vaporization chamber, causing explosive vaporization, and, consequently, causing a droplet of ink to be ejected through an associated orifice onto the paper.
In U.S. application Ser. No. 07/862,668, filed Apr. 2, 1992, entitled "Integrated Nozzle Member and TAB Circuit for Inkjet Printhead," a novel nozzle member for an inkjet print cartridge and method of forming the nozzle member are disclosed. This integrated nozzle and circuit design is superior to the orifice plates for inkjet printheads formed of nickel and fabricated by lithographic electroforming processes. A barrier layer includes vaporization chambers, surrounding each orifice, and ink flow channels which provide fluid communication between an ink reservoir and the vaporization chambers. A flexible electrical conductor having conductive traces formed thereon has formed in it nozzles or orifices by Excimer laser ablation. Throughout this document, the terminology "electrical conductor" is used generally to refer to a well-known kind of multiconductor flat cable, sometimes called a flex circuit, that is made up of a flat, insulating polymeric tape and multiple narrow, extremely thin, conductive metallic strips carried on the tape. By providing the orifices in the electrical conductor itself, the novel method over comes the shortcomings of conventional electroformed orifice plates. The resulting printhead subassembly having orifices and conductive traces may then have mounted thereon a substrate containing ink ejection elements associated with each of the orifices. The leads at the end of the conductive traces formed on the back surface of the printhead subassembly are then connected to the electrodes on the substrate and provide energization signals for the ink ejection elements.
An existing solution for bonding the conductive traces formed on the back surface of the printhead subassembly to the electrodes on the substrate includes the solderless electrical connection of two contact elements by using a laser light beam attached to a fiber optic system which directs the light to the spot to be bonded. The method results in solderless gold to gold compression bonding of conductive leads on a polymer flex circuit tape, such as a polyamide, without damaging the tape. A strong solderless gold to gold bond can be formed between the gold plated copper lead on the flex circuit tape and a gold plated pad on a semiconductor chip. As with all bonding procedures a method for determining bad or low strength bonds is required. Damaged bonds or low strength bonds are usually detected by a sampling plan. This method utilizes shear tests to measure low bond strength. This is a destructive test and must consume a small number of samples. Another method to detect a bad bond utilizes an IR feedback to report any damage to the bond as a result of burning. This is a non-destructive method, however, it is only capable of detecting a burned bond. A low strength bond may not be detected by this method.
One principal cause of low strength bonds is use of a damaged optical fiber. Accordingly, it would be advantageous to have a process to predict and eliminate bad or low strength bonds caused by optical fiber damage during laser TAB bonding process without destructive testing.